Known rotor spinning machines include many spinning stations. Each is sometimes referred to as a "spinning box." A sliver or a fiber strip is applied to each such station. A so-called feed trough is located at the entrance to each spinning station to receive the fiber strip and press it against a rotating feed roller, so that the fiber material will be drawn over the feed trough by the feed roller. The feed trough can be constructed as a type of lever or flap which is pivotally mounted and extends in the vicinity of the feed roller approximately tangentially thereto. After the feed roller, the fiber material is taken up by a separating roller where the fibers are separated.
The weight of fibers advanced per unit of time by the feed roller is an important factor with respect to the size of the yarn produced at the spinning station of a rotor spinning machine. Also, the uniformity of the mass of fibers along the length of the strip forming the input to the spinning station is an important factor with respect to the uniformity of the resulting yarn. However, if the thickness or mass of the fiber material is to be measured in the vicinity or region of a spinning station, then it is necessary to arrange measuring devices, such as measuring hoppers etc., upstream or downstream of the spinning station. But, this can only be done where space for a measuring device is available along the route of the supplied fiber material. If this space is available, a measuring device can be provided. However, this generates resistance in the fiber material which needs to be overcome and which can influence the fiber material in an unexpected manner.